Various USB (Universal Serial Bus) connectors and related standards have been developed. Recently, a USB Type-C standard has been developed having various requirements for USB Type-C connectors and the operation of devices implementing USB Type-C connections. Once two USB Type-C devices have completed connection negotiations and are connected through a USB Type-C connection, one device will operate as a DFP (downward facing port) device while the other device will operate as a UFP (upward facing port) device. It is also noted that these roles can be swapped based upon additional communications between the two devices. The USB Type-C standard is described, for example, in the USB Type-C Cable and Connector Specification (v1.1) released in 2015.
For the physical connection, the USB Type-C standard provides a variety of potential physical connection types including a Type-C plug and a Type-C receptacle. The Type-C plug is symmetrical and can be inserted into the Type-C receptacle in two orientations. As such, the USB Type-C standard includes an orientation detection procedure so that a device having a Type-C receptacle can determine the orientation for an inserted Type-C plug from another device. While there are a variety of connections in the USB Type-C connection, two of these connections are the VCONN (connection power) connection and the CC (configuration channel) connection. The CC connection is used for cable orientation detection as well as configuration and management of connections across a USB Type-C cable. The VCONN connection is used to power active or electronically marked cables. In some applications, such as with VCONN powered accessories, the power from the VCONN connection provides the only power source. In other applications, such as with cell phones, the power from the VCONN connection is used to run low-power features.
In part, the USB Type-C specification requires a UFP device in dead-battery or unattached modes to pull down a small resistance (Ra) on the VCONN connection to ground. Dead-battery mode is a condition where no supply is present or being applied to the UFP device so that the UFP device is an unpowered device. As set forth in the USB Type-C specification, attached mode includes states after two USB Type-C devices have established a connection, and unattached mode includes states when a USB Type-C device is waiting to be detected to establish a connection to another USB Type-C device. The resistance (Ra) can be detected by a DFP device, for example, by injecting a small current (Ip) directly to the VCONN connection between the devices or by pulling a small resistance (Rp) to a supply voltage (Vp) on the VCONN connection between the devices. A similar small current (Ip) or small resistance (Rp) pulled to a supply voltage (Vp) is also provided by the DFP device on the CC connection. The DFP device then monitors voltages on both the VCONN connection and the CC connection to determine device orientation and operational modes. For example, when the DFP device detects the presence of the VCONN resistance (Ra), the DFP device can then provide VCONN power to the UFP device through the VCONN connection. As the voltage on the VCONN connection is relatively small before the DFP device applies power to the VCONN connection and as there is no other voltage source in dead-battery modes, the USB Type-C specification becomes difficult to achieve with CMOS transistors.